The gate is marked on this 18th century map, between Ludgate Hill and Ludgate Street: http://www.motco.com/Map/81002/SeriesSearchPlat...
View of Ludgate before its demolition in 1760 with text on its history. © City of London http://collage.cityoflondon.gov.uk/collage/app?...
Ludgate, one of the four ancient gates of the City, taken down November 1760, at the solicitation of the inhabitants of Farringdon Within and Farringdon Without . It stood immediately west of the church of St. Martin, Ludgate, between the church and the London Coffee-house. It is a popular notion that Ludgate takes its name from the mythical King Lud, by whom it was built sixty-six years before the birth of Christ . Dr. Edwin Freshfield supposes it to be derived from the word lode, a cut or drain into a larger stream.
---London, Past and Present. H.B. Wheatley, 1891.
Ludgate, is situated 797 feet south of Newgate, and according to Geffry of Monmouth, took its name from King Lud; but as that historian has justly forfeited all credit among the learned, his assertion has no weight; for it is certain that the ancient Britons had no walled towns. The name of this gate is therefore with much greater propriety derived from its situation near the rivulet Flood, Flud, Vloet, Fleote or Fleet, which ran into Fleet Ditch.
The present gate was erected in the year 1586, with the statue of Queen Elizabeth on the west front, and those of the pretended King Lud, and his two sons Androgeus and Theomantius or Temanticus on the east.
---London and Its Environs Described. R. Dodsley, 1761.
Some images of Ludgate: http://en.wikipedia.org/wiki/Ludgate#mediaviewe...
Chart showing the number of references in each month of the diary’s entries.